Potatoes to be used for seed pieces from which commercial quantities of potatoes are to be grown the following year, are grown specifically for that purpose for sale to growers. The commercial potato grower typically buy these seed potatoes just before planting. Small (e.g., 11/2" diameter) seed potatoes are typically planted whole, 2" seed potatoes are cut in two, and larger seed potatoes are cut into thirds or quarters so that two "eyes" are present on each piece. Ideally, each seed piece weighs from 2 to 3 ounces. After the seed pieces have been cut, they may be treated with a rot/disease prevention dust.
Thereafter, the cut and treated seed pieces are planted in springtime in a hill formed by a planter, at a depth of from 3" to 9" and about 1' apart. As the seed pieces are placed in the ground by the planter, they are usually sprayed with a blight prevention compound and/or other disease-preventing pesticide(s).
Potatoes require significant amounts of nitrogen, and so a banded mixture of nitrogen, phosphorus, and potassium fertilizers are typically added to the soil near where the seed piece is to be planted just prior to or at planting. Then, about a week after plants emerge in mid- to late-May, another nitrogen fertilizer application is often made, for example, by dripping liquid urea ammonium nitrate of from 28% to 32% nitrogen onto the sides of the hill or applying a granular ammonium nitrate onto the sides of the hill. A hiller attachment then throws soil onto the sides of the hill to cover the newly-applied nitrogen fertilizer. This process is typically repeated a second time 7-10 days later. By this time, the potato plants will have become too large to send the fertilizer/hiller equipment through the fields. So, if further nitrogen supplements are required, a liquid nitrogen fertilizer such as liquid urea ammonium nitrate is sent through the irrigation water. Various herbicides, insecticides and fungicides may also be applied throughout the growing season, depending upon the need to prevent crop damage from various weeds, insects, diseases, and other problems.
Most commercial potato growers use central pivot irrigation systems to irrigate their crops, although irrigation scheduling varies. Growers typically irrigate in the absence of adequate rainfall, applying from 0.25 to 0.75 inches of water at a time, depending on need. In Wisconsin, growers may use the Wisconsin Irrigation Scheduling Program (WISP) to determine irrigation requirements. This program takes into account temperature, crop cover, evaporation, and transpiration to determine water deficit. Growers also use visual observation of plant water stress to determine irrigation needs. Because potatoes are especially sensitive to drought at tuber-setting time (i.e., when plants flower, and just after), irrigation is indicated when visual indications of water stress or soil dryness become present at tuber-setting time.
Whether irrigating according to a schedule or in response to visual indications of water stress or soil dryness, irrigation water may solubilize nitrogen and other fertilizers present in the soil and leach these compounds away from the potato plants. This is problematic not only because the potato plants will not benefit from needed fertilizer, but also because the groundwater can become contaminated with the excess fertilizer. There is added uncertainty because the potatoes being grown are not visible to the grower, making conditions actually present around the plant roots and adjacent the growing potatoes is not precisely known.
Referring now to FIG. 1, it can be seen that in an attempt to create better infiltration of the soil of a potato hill 22 by water for access by potato plant 20, growers may use surfactants 24 applied through an overhead sprinkler irrigation system. Surfactants 24 are conventionally broadcast in this manner 1 week to 10 days after emergence, with application of the first nitrogen fertilizers. This prior art technique is believed to create a surfactant distribution like that schematically illustrated in FIG. 1, in which the surfactant is believed to cover the hill and to pool in the furrows 26 between the hills. It is postulated by the inventor hereof, that this surfactant distribution actually leads to increased nitrate leaching.
It can thus be seen that a need remains for a safe and economical technique which minimizes soil dryness and water stress in potato plants. There also remains a need for techniques and compositions which minimize nitrate leaching in potato crop acreage and maintains a supply nutrients to growing potato plants for maximum crop yield. It is therefore against the background described above that the advances of the present invention have been made.